In some piston systems it is desirable to operate two pistons coupled to a common drive mechanism at different speeds. This is typically achieved by linking two different crankshafts together by a geared drive mechanism which runs the camshafts at different speeds such that two pistons may be driven at different speeds by the respective camshafts. This arrangement is, however, comparatively heavy and complex, and requires provision of an entirely separate crankshaft, leading to difficulties in providing a compact engine arrangement. It is therefore desirable to provide a piston system which overcomes these disadvantages.